fix REPL completions not always being unique (#28694)

* fix REPLcompletions not unique, fix #28692

(cherry picked from commit cd5e5a3)

stdlib/REPL/src/REPL.jl

@@ -346,22 +346,22 @@ function complete_line(c::REPLCompletionProvider, s)
     partial = beforecursor(s.input_buffer)
     full = LineEdit.input_string(s)
     ret, range, should_complete = completions(full, lastindex(partial))
-    return map(completion_text, ret), partial[range], should_complete
+    return unique!(map(completion_text, ret)), partial[range], should_complete
 end
 
 function complete_line(c::ShellCompletionProvider, s)
     # First parse everything up to the current position
     partial = beforecursor(s.input_buffer)
     full = LineEdit.input_string(s)
     ret, range, should_complete = shell_completions(full, lastindex(partial))
-    return map(completion_text, ret), partial[range], should_complete
+    return unique!(map(completion_text, ret)), partial[range], should_complete
 end
 
 function complete_line(c::LatexCompletions, s)
     partial = beforecursor(LineEdit.buffer(s))
     full = LineEdit.input_string(s)
     ret, range, should_complete = bslash_completions(full, lastindex(partial))[2]
-    return map(completion_text, ret), partial[range], should_complete
+    return unique!(map(completion_text, ret)), partial[range], should_complete
 end
 
 mutable struct REPLHistoryProvider <: HistoryProvider

stdlib/REPL/test/replcompletions.jl

@@ -102,6 +102,11 @@ let s = ""
     @test s[r] == ""
 end
 
+let s = "using REP"
+    c, r = test_complete(s)
+    @test count(isequal("REPL"), c) == 1
+end
+
 let s = "Comp"
     c, r = test_complete(s)
     @test "CompletionFoo" in c